[heap] Don't create a filler object when setting up a LAB

The LocalAllocationBuffer (LAB) doesn't need to be iterable, when the
heap needs to be iterable we have explicit calls to `MakeIterable()`
anyways for the LABs.

Also creating that filler object initially isn't enough, we would need
to do this after each and every allocated object.

Change-Id: Iedb011205d7590a75ea17d518e78e340f1d4b63d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3270546
Commit-Queue: Victor Gomes <victorgomes@chromium.org>
Auto-Submit: Victor Gomes <victorgomes@chromium.org>
Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77819}

src/heap/spaces.cc

@@ -325,14 +325,7 @@ void LocalAllocationBuffer::MakeIterable() {
 LocalAllocationBuffer::LocalAllocationBuffer(
     Heap* heap, LinearAllocationArea allocation_info) V8_NOEXCEPT
     : heap_(heap),
-      allocation_info_(allocation_info) {
-  if (IsValid()) {
-    heap_->CreateFillerObjectAtBackground(
-        allocation_info_.top(),
-        static_cast<int>(allocation_info_.limit() - allocation_info_.top()),
-        ClearFreedMemoryMode::kDontClearFreedMemory);
-  }
-}
+      allocation_info_(allocation_info) {}
 
 LocalAllocationBuffer::LocalAllocationBuffer(LocalAllocationBuffer&& other)
     V8_NOEXCEPT {